Attempting to layer two materials on the same parts of a mesh
You can use the following steps : 


create two UV maps in the vertex panel 





create a material for all faces of the hull like this :




A diffuse BSDF (for the hull details) and a Emission BSDF (for the windows ligght) are added together (using a Mix BSDF should be better). The strength of the emission BSDF is increased to 10. The diffuse BSDF is connected with the hull details image which is connected to the UV map of the hull. The Emission BSDF is connected with the windows light image which is connected to the UV map of the window.


Unwrap the hull on the hull image like this (note that windows are painted with black)





Unwrap the windows on a white part of the windows light image. Then unwrap all other faces on a black part (they are all stacked in the orange square at the bottom)




The size of the windows light can be very small (256px x 256px) because it contains only white and black surfaces.

Here is a final render : 



If you add an object near the window, you will see that it will be lighted by the window light.